Method and device for producing molds for toothed belts

ABSTRACT

The invention relates to a method and to a device for producing molds for toothed belts. A grinding wheel ( 9 ) that has a profiled periphery is used instead of a milling cutter to provide the circumference of a roller-shaped blank ( 4 ) with the matrix of a desired tooth contour of a toothed belt. The circumferential profile of the grinding wheel ( 9 ) is trimmed using a CNC-controlled diamond trimming pin ( 11 ) or alternatively with a profiling diamond ( 19 ).

The present invention relates to a method and a device for producingmolds for toothed belts.

Molds for toothed belts are typically tubular steel rollers which aretoothed linearly on their peripheral surface and are required as aninner core in the production of toothed belts, from Perbunan rubber orplastic, for example. The heated toothed belt material is pressed intothe teeth of the mold for toothed belts. The toothing of the molds fortoothed belts thus forms the matrices of the toothed belt toothing.

Producing molds for toothed belts from cylindrical blanks by milling isknown. The requirements for the precision of the tooth geometries oftoothed belts have increased enormously. Thus, the tooth surface is tobe as smooth as possible, i.e., if possible, is not to have any imagingof the milling marks present in the molds for toothed belts.

Post-treatment of the surface of the molds for toothed belts istherefore typically necessary if the molds for toothed belts are milled.In addition, the multiplicity of tooth geometries has increased, whichis to meet the demands for higher performance and quiet running.

It is thus the object of the present invention to provide a method and adevice of the type initially cited, using which, in addition to highgeometrical precision, high surface quality of the molds for toothedbelts is made possible.

This object is achieved in a method in which, using a metal-cuttingtool, a matrix of the desired toothed belt toothing is incorporated intothe circumference of a workpiece, which is essentially cylindricalbefore processing, in that at least one rotating grinding wheel having aprofiled circumference is used as the metal-cutting tool, the peripheralprofile corresponding to the profile of a complete tooth groove of thedesired mold for toothed belts.

Therefore, the matrix for the toothed belts is not milled, but generatedby grinding using specially profiled grinding wheels with a grindingmotion parallel to the lengthwise central axis of the workpiece. In thisway, a quality of the surface of the finished workpiece may be achievedwhich makes post-treatment unnecessary. The complete region from thehead of one tooth to the head of the neighboring tooth is understood asa tooth groove. The grinding of two neighboring tooth grooves thus leadsto a complete tooth of the mold for toothed belts being produced, i.e.,the outer diameter of the mold for toothed belts is also ground. Thecontraction of the toothed belt material during cooling in theproduction process must be taken into consideration for the geometry ofthe tooth groove of the mold for toothed belts.

The use of profiled grinding wheels also allows extremely finesubstructures to be generated easily in the tooth profile, e.g., a wavedsub-profile in the region of the tooth flanks. For example, channelsrunning parallel to the axis of the mold for toothed belts may beintroduced into the profile for this purpose. Toothed belts havingsub-profiles of this type are disclosed in German Patent 199 08 672 C1.

The method according to the present invention may also be implemented sothat the peripheral profile of the grinding wheel is produced and/ortrimmed using a CNC-controlled trimming pin. The trimming procedure isnecessary due to the gradual wear of the grinding wheel. The CNCcontroller allows nearly any arbitrary profile to be introduced andtrimmed highly precisely around the circumference of the grinding wheeland thus allows the production of varying tooth geometries in arelatively simple way.

The method according to the present invention may also be implemented sothat the peripheral profile is produced and/or trimmed on a profiledtrimming element having a profiled trimming region. In this case, a CNCcontroller may be dispensed with for the trimming, since the profiledtrimming region provides a fixed profile. This may be particularlyadvantageous if high piece counts having identical tooth geometries areto be produced.

Finally, the method according to the present invention may also beimplemented so that the trimming of the rotating grinding wheel and thesubsequent grinding of the workpiece are performed in one single lineartranslational movement of the grinding wheel relative to the workpiece.This may be achieved through suitable positioning of the profiledtrimming element. If high-precision positioning and adjustment of theprofiled trimming element relative to the workpiece has been performed,the line of the profile of the trimming region of the trimming elementprovides the cutting shape exactly for each grinding procedure, i.e.,the trimming region must lie exactly in the alignment of the desiredcutting line. After the geometry of a tooth groove has been ground intothe workpiece, the workpiece is rotated by an angle corresponding to thereference circle graduation of the tooth geometry. The grinding wheel isguided over the trimming region of the trimming element for re-trimmingand, in a continuation of a linear translational movement, to theworkpiece for the next grinding procedure. Starting from the assumptionthat the trimming region was not worn to a significant degree, thegrinding wheel is always at the correct relative height in relation tothe workpiece after the trimming. Any possible appearance of wear at thetrimming region may be compensated for through manual or automaticadjustment.

The relative movement between the grinding wheel and workpiece may beachieved through a movement of the grinding wheel in relation to amachine stand or a movement of a toolholder.

The object cited above is achieved for a device, comprising a workpieceholder, means for rotation, using which at least one essentiallycylindrical workpiece clamped in the workpiece holder is rotatable by apredetermined angle around its longitudinal axis in a controlled way,and a metal-cutting tool movable relative to the workpiece holder, inthat the at least one tool is a grinding wheel, and trimming means areprovided for trimming a specific peripheral profile of the at least onegrinding wheel, the peripheral profile of the grinding wheel able to betrimmed in such a way that it corresponds to the profile of a completetooth groove of the desired toothed belt toothing.

The device according to the present invention may also be implemented sothat the trimming means includes at least one trimming pin, which has ahard body on its point facing the grinding wheel circumference, the hardbody being movable relative to the associated grinding wheel both in theaxial direction and in the radial direction in regard to the grindingwheel and being controllable using a programmable control unit.

For trimming, the trimming pin moves around the circumference of therotating grinding wheel with its hard body, e.g., a diamond. Nearly anyarbitrary profile shape may be produced using a CNC controller.

Furthermore, it may be advantageous to implement the device according tothe present invention so that the at least one trimming pin isadditionally pivotable around a trimming pivot axis, which isperpendicular to the axial and radial directions and runs through thehard body. The trimming pivot axis provides an additional variationpossibility for the desired profile shapes. The hard body typically hasa cross-section in the shape of a circular arc, at least in its regionprovided for processing workpieces. The trimming pivot axis then runsperpendicularly to this cross-section, through the center of the hardbody in relation to the radius of the circular arc.

The device according to the present invention may also be implemented sothat the trimming means comprise at least one profiled trimming elementhaving a profiled trimming region, the profile of the trimming regionbeing the counter profile of at least a part of the desired peripheralprofile of the at least one grinding wheel.

This variant has the advantage that a complicated CNC controller is notnecessary for the movement of the trimming means. A profiled trimmingelement is expedient particularly if variations of the profile shape arenot necessary.

Furthermore, it may be advantageous to implement the device according tothe present invention so that the profiled trimming element is atrimming hard body, made of diamond, for example, having an edge-liketrimming region.

The device according to the present invention may, however, also beimplemented so that the profiled trimming element is a rotatabletrimming roller having a rotationally-symmetric trimming region.

The grinding wheel must always be strong enough to be able to achievegood removal with high surface quality on the workpiece. However, thegrinding wheel material must still be soft enough that it does not wearthe means used for trimming.

Finally, the device according to the present invention may also beimplemented so that the at least one profiled trimming element ispositioned and may be adjusted in relation to the workpiece holder insuch a way that, viewed in the direction of the lengthwise central axisof the at least one clamped tool, the projection of the profile of thetrimming region onto a tool face corresponds to the profile of thecross-section of the cut desired during a grinding procedure.

With such an arrangement, it is possible, using one single lineartranslational movement, to first guide the rotating grinding wheel alongthe profiled hard body and achieve the desired trimming of theperipheral profile of the grinding wheel at the same time, andsubsequently perform the grinding procedure on the workpiece. Adjustmentof the grinding wheel to the lengthwise central axis of the workpiece inthe radial direction is therefore no longer necessary for the grindingprocedure. In addition, it is completely unimportant how much is removedfrom the diameter of the grinding wheel during the trimming procedure,since the trimming edge profile or the profile of the profiled roller isexactly in alignment with the cut desired during the grinding procedure.

In the following, the present invention is explained on the basis offigures.

FIG. 1 schematically shows a grinding device in a side view,

FIG. 2 schematically shows a detail of a grinding wheel and a mold fortoothed belts during the grinding procedure,

FIG. 3 schematically shows a grinding wheel during the trimming,

FIG. 4 schematically shows a further grinding device having a fixedprofiling diamond, and

FIG. 5 schematically shows partially a profiling diamond.

FIG. 1 shows a grinding device having a machine stand 1, to which ahorizontally movable grinding table 2 is attached. The grinding table 2supports a workpiece holder 3, in which the roller-shaped blank 4 for amold for a toothed belt is clamped between an apparatus part 16 and anouter support 17. The blank 4 may be rotated around a horizontal axis ofrotation 7 in a controlled way via a rotating driver 5 using a rotatingplate 6. The axis of rotation 7 simultaneously forms the lengthwisecentral axis of the blank 4 in the blank 4. The workpiece holder 3includes a high-precision direct measurement system (not shownseparately here), which allows precise rotational angle setting. Agrinding wheel 9 is rotatably attached to a grinding wheel holder 8above the workpiece holder 3. The grinding wheel holder 8 may be movedhighly precisely in a controlled way in the vertical direction. In orderto obtain a mold for toothed belts from the blank 4, the counter profileof the toothed belt toothing must be worked into the circumference ofthe blank 4, the toothing being linear and constant in the direction ofthe lengthwise central axis of the blank 4. Viewed in cross-section, thecircumference thus forms the matrix for the toothed belt toothing.

The grinding wheel 9 has a profile 10 around its circumference, which isshown in an enlarged view in FIG. 2. The peripheral profile 10 of thegrinding wheel 9 corresponds to the desired profile of a tooth groove ofthe mold for toothed belts. To produce the mold for toothed belts, theblank 4 is moved using the grinding table 2 while the grinding wheel 9is lowered in such a way that the grinding wheel 9 cuts the matrix for acomplete tooth of the toothed belt into the blank 4 over the entirelength of the blank 4. Subsequently, the blank 4 is rotated by apredetermined angle α and the next tooth matrix is produced. The outerdiameter of the blank 4 is also ground during each grinding procedure,so that the entire peripheral surface is ground in a finished mold fortoothed belts.

Since the grinding wheel 9 wears down with increasing use, theperipheral profile 10 of the grinding wheel 9 is re-trimmed using atrimming pin 11 before each grinding procedure. This is performed withthe aid of a CNC process. The trimming pin 11 is movable in the axialand radial directions in relation to the rotational axis of the grindingwheel. In addition, the trimming pin 11 also has a trimming pivot axis12, which runs essentially perpendicular to the axial and radialdirections and through the center of a round diamond 13 on the tip ofthe trimming pin 11. Equipped with these degrees of freedom, nearly anyarbitrary profile may be introduced into the circumference of thegrinding wheel 9 using the trimming pin 11. In particular, it ispossible to introduce fine substructures into the peripheral profile 10.Precisions of up to +/−0.01 millimeter may be achieved. In order toachieve this precision, it may be advisable to provide a variableadvance speed of the trimming pin 11, so that, for example, a loweradvance speed is used in the regions of smaller radii in the peripheralprofile 10. Furthermore, a virtual diamond radius may be preset for theCNC controller. In this way a constant deviation from the ideal line inthe profile line may be easily corrected, for example, without having tochange the entire CNC programming.

The grinding wheel is continuously cleaned with the aid of a pair ofspray nozzles 14 (FIG. 1), which reach both sides of the peripheralprofile 10 sufficiently uniformly, for the trimming procedure.

During the grinding procedure, a further pair of spray nozzles 15 isused, which cleans the grinding wheel 9 at high pressure and thusprevents it from clogging. The pair of nozzles 15 is positioned indirect proximity to the grinding wheel 9.

In order to make the entire process cost-effective, it may be expedientto prepare the blank 4 using known milling machines, so that thegrinding wheel 9 wears less.

FIG. 4 shows an alternative construction of a grinding device. Partscorresponding to one another are provided with the same referencenumbers in different figures. The blank 4 a is shorter in FIG. 4 than inFIG. 1. The workpiece holder 3 has the same spacing in its apparatusparts 16 and 17 as in FIG. 1. However, it is provided with a lengthadapter 18, which has struts 20. With the aid of one or more lengthadapters 18, adjustment of apparatus parts 16 and 17 of the workpieceholder 3 may be avoided even in the event of different lengths of blanks4 a, in order to maintain high precision in the spacing, which isachieved once in a complicated way.

A profiling diamond 19, which is used for trimming the grinding wheel 9and is shown enlarged in FIG. 5, is positioned on the outer support 17.The profiling diamond 19 has a trimming edge 21, whose profilecorresponds to the profile of the desired tooth groove of the mold fortoothed belts. Before a grinding procedure, the grinding table 2 isbrought into the starting position, in which the grinding wheel 9 ispositioned to the left of the profiling diamond 19 in FIG. 4. Thegrinding wheel holder 8 is then lowered enough that during movement ofthe grinding table 2 to the left (in FIG. 4), the outer circumference ofthe rotating grinding wheel 9 is provided with the corresponding counterprofile by the trimming edge 21 of the profiling diamond 19. The outercircumference of the grinding wheel 9 thus obtains the profile of acomplete tooth groove of the desired mold for toothed belts.

The profiling diamond 19 is aligned in such a way that, through furthermovement of the grinding table 2, the grinding wheel reaches theworkpiece 4 a in the correct operating position without a verticalchange in position and produces the matrix for a complete tooth of thetoothed belt, including the tooth root, in one single grindingprocedure. Subsequently, the grinding wheel holder 8 is raised and thegrinding table 2 is moved back to the starting position. The grindingwheel holder 8 is lowered again, however, it is lowered slightly morethan for the preceding pass due to the wear caused during the grindingprocedure. In this way, the circumference of the grinding wheel 9 isnewly trimmed before each grinding. Since the position of the trimmingedge 21 remains unchanged in relation to the axis of rotation 7, it isadditionally ensured that the grinding wheel 9 again reaches theworkpiece 4 a in the correct operating position and the matrices of thetoothed belt teeth ground into the workpiece 4 a are exactly identicalin regard to the tooth geometry and the tooth height. In this way, thecomplete circumference of the mold for toothed belts, including theouter diameter, is ground using the grinding wheel 9.

The profiling diamond 19 is attached so its position may be changed inthe vertical direction, in order that possible wear may be compensatedfor or adjustment to a different workpiece diameter is possible.

List of reference numbers 1 machine stand 2 grinding table 3 workpieceholder 4 blank 5 rotating driver 6 rotating plate 7 axis of rotation 8grinding wheel holder 9 grinding wheel 10 peripheral profile 11 trimmingpin 12 trimming pivot axis 13 diamond 14 pair of spray nozzles 15 nozzle16 apparatus part 17 outer support 18 length adapter 19 profilingdiamond 20 strut 21 trimming edge

1. A method of producing molds for toothed belts comprising: obtaining aworkpiece, said workpiece being cylindrical and having a longitudinalaxis and a circumferential surface; obtaining a metal-cutting tool, saidcutting tool having at least one rotating grinding wheel, said grindingwheel rotating about an axis perpendicular to said longitudinal axishaving a profiled circumferential surface, said profiled circumferentialsurface comprising a convex central region; applying said rotatinggrinding wheel against the workpiece circumferential surface andsimultaneously translating the workpiece along the longitudinal axis ofthe workpiece for forming a matrix of tooth belt toothing into saidcircumferential surface of said workpiece, said matrix of toothingcorresponding to said profiled circumferential surface.
 2. The methodaccording to claim 1, further comprising: obtaining a CNC controlledtrimming pin; and trimming said profile onto said circumferentialsurface grinding wheel with said CNC controlled trimming pin.
 3. Themethod according to claim 1, further comprising: obtaining a profiletrimming element, said trimming element having a profiled trimmingregion; and trimming said profile circumferential surface onto saidgrinding wheel with said trimming region of said profiled trimmingelement.
 4. The method according to claim 3, comprising: trimming saidrotating grinding wheel and grinding said workpiece in a single lineartranslational movement of said grinding wheel relative to saidworkpiece.
 5. A device for producing molds for providing toothedmatrices on a cylindrical workpiece, having a circumferential surfaceand a longitudinal axis, said device comprising: a workpiece holder,said workpiece holder holding said workpiece; rotating means forangularly rotating said workpiece about said longitudinal axis on saidworkpiece holder; a cutting tool including a grinding wheel having arotating axis perpendicular to said longitudinal axis and having aprofiled circumferential surface, said profiled circumferential surfacecomprising a convex central region; means for translating saidwork-piece along said workpiece longitudinal axis; trimming means fortrimming a profiled circumferential surface onto said grinding wheel,said profiled circumferential surface comprising a peripheral profiledefining a counter profile for a toot for a toothed belt; said trimmingmeans comprising a profiled trimming element, said profiled trimmingelement having a profiled trimming region, said profiled trimming regionhaving a counter profile of said profiled circumferential surface ofsaid grinding wheel.
 6. The device of claim 5 wherein said profiledtrimming element is a diamond.